Submenu in Arcade Basic such as in Gridiculous

Hi guys!

I’m using c.bavota Arcade Basic theme, everything is ok but one function, I would like to have submenu like in Gridiculous theme:
https://demos.bavotasan.com/gridiculous/

I mean this Sample Page -> Child Page 01 (this is last which I can do) -> Child Page 02 – this I can’t add, I know how to make such menu but, in other themes it works perfectly but here I can’t see it.

page that I’m using arcade basic is https://www.top-light.pl I would like to have main categories in my menu.